In a conventional magnetic proximity switch, an armature having a center contact is biased by a spring on the side of normal closing contact to retain the contact between a center contact and the normal closing contact, while a permanent magnet is brought near to the switch from outside thereof to pull the armature to the side of normal opening contact against the biasing force of said spring thus to contact both contacts so as to contact the center contact with the side of normal opening contact.
Namely, as shown in FIG. 1, within a case 1 made of synthetic resin and the like, one side of a center contact 3 mounted on an armature 2 is biased by a spring 4 on the side of normal closing contact 5 to retain the contact between both contacts. A permanent magnet 7 may be brought near to the case from the outside (from above in FIG. 1) to pull the armature 2 against the biasing force of the spring 4 thus to contact the center contact 3 with normal opening contact 6.
However, said conventional magnetic switch has disadvantage that when the spring 4 takes large elasticity to enhance contact pressure of both contacts at the time of normal closing, the switch does not work unless the permanent magnet is brought nearer to the case 1 or the magnetic force of the permanent magnet itself is made larger. In short, there is involved a conflicting problem that when positive contact between both contacts at the time of normal closing is assured, the working sensitivity of the switch (the distance between the switch and the permanent magnet) becomes poor.